Ultrasonic blade design for scoring double angle groove and products therefrom

ABSTRACT

The present invention relates to the formation of a double angle V-groove in the backside of plastic shells to provide a preweakened section for a vehicle application. The double angle V-groove may be located at the airbag deployment opening of a vehicle.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional ApplicationSerial No. 60/411,458, filed Sep. 17, 2002, and is herein incorporatedby reference.

FIELD OF THE INVENTION

[0002] The present invention relates to a method for scoringdouble-angle weakening grooves in skin material and products producedtherefrom. The invention has particular utility in the field ofautomotive applications, specifically, the backside of skin sectionscovering airbag deployment systems

BACKGROUND OF THE INVENTION

[0003] A common type of interior trim panel or cover used to cover andhide the air bag in a motor vehicle may comprise a thin elastic plasticouter skin having a non-glaring grained outer surface, a rigid retaineror substrate and an intermediate layer of soft plastic foam between theskin and substrate. In some cases the foam is omitted.

[0004] It is common practice to use vinyl, typically polyvinyl chloride(PVC), to form the thin plastic outer shell or skin for the panel. Theskin material may also comprise urethanes (e.g., PU), olefins (e.g., PP,PS, TPO, ETP-TPO), esters (e.g., COPE), styrenes (e.g., AAS, ASA) andrubbers (e.g. TPO, ETP-TPO, ABS) in various compositions.

[0005] The present invention relates to those trim panels or coverswherein the skin is formed of a thermoplastic polymer or thermosettingresin and is provided with an invisible tear seam, and the substrateincludes one or more doors that are impacted by the inflating air bagand press against the cover to separate the tear seam and then swingoutward to form an opening in the cover for deployment of the air baginto a protective position in the passenger space. These tear seams areprovided in various configurations or patterns with the most commonhaving a C, H, U, or X-shape and wherein the pattern determines thenumber of doors required in the substrate.

[0006] To develop tearing and/or breaking, air bag doors that areintegrally formed with automotive trim or instrument panels willsometimes include regions of weakened materials, reduced thickness orscoring, all of which are commonly referred to as “tear seams”. Tearseams are weakened areas designed to preferentially tear and/or breakwhen an air bag inflates and forces the doors to open.

[0007] It is desirable that the tear seams and thereby the presence ofthe air bag be hidden from view for various reasons and heretofore, thishas been accomplished in several different ways. Such a tear seam iscommonly referred to as an “invisible tear seam”. One way of providingsuch an invisible tear seam is by forming a tear seam defining groove orseries of depressions in the backside of the skin. This leaves a thinand thereby weakened section at the outer or appearance side of the skinthat defines the tear seam without outwardly revealing its presenceduring normal view by an ordinary vehicle occupant. Examples of suchinvisible air bag cover tear seams are disclosed in U.S. Pat. Nos.5,072,967; 5,082,310; 5,316,822; 5,348,339; 5,632,914; 5,863,064 and5,961,143.

[0008] A variety of disclosures exist directed at preweakening a skinsection employed in an automotive airbag deployment system.

[0009] U.S. Pat. Nos. 4,524,894 and 4,805,390 are directed at the use ofan apparatus for cutting patterns and a groove cutting machine toprovide a constant thickness of material remaining after the cuttingprocess.

[0010] U.S. Pat. Nos. 5,803,489 and 5,968,381 are directed to an air bagcover with a tear line with a predetermined wall thickness which tapersfrom the inside towards the outside with a width of 120-190 microns.

[0011] U.S. Pat. No. 6,308,391 discloses a method of producing V-shapedgrooves machines in the surface of different materials. The V-shapedgrooves have a predetermined depth relative to the surface. The V-shapedgrooves are of a single angle.

[0012] Other background disclosures include U.S. Appln. Ser. Nos.10/027,779; 09/778,394; 10/251,897; 10/241,366; GB 2,276,354; JP6218811; and EP 1177878.

[0013] When soft plastic or elastomeric skin materials are used as acover skin for an air bag deployment system, it is not uncommon for theskin material that forms the invisible tear seam in the backside of thecover skin to heal or stick together if an insufficient amount ofmaterial is not removed when the tear seam is formed. Thus, the angle ofthe side walls of the seam is critical. Additionally, some higherpowered laser weakening systems may cause degradation of the skinsurface where it has been thinned or weakened, resulting in a tear seamthat remains tacky. A further issue with these systems is the smokeproduced, making the work area quite unpleasant.

[0014] An alternate method to laser weakening involves the use of aknife-blade which may score the backside of the cover skin to a knowndepth, thus providing a line of mechanical weakness or tear seam. Theknife blade may be heated or excited by another source of energy such asultrasonics to provide a reliable cut or scoring line. The scoring neednot be a continuous groove but may be intermittent and vary in depthdependent on where the tearing of the seam is desired to initiate andpropagate.

[0015] It is therefore desirable to provide a knife-blade design thatprevents healing of the tear seam, particularly for soft elastomericskin materials.

SUMMARY OF THE INVENTION

[0016] The present invention relates to a blade design for scoringdouble angle V-grooves in the backside of plastic shells to provide apreweakened section. The double angle V-groove may be located at theairbag deployment opening of a vehicle.

[0017] It is therefore an object of the present invention to provide aknife-blade having a double angle design which allows for the removal ofsufficient material from the tear seam to prevent healing of the sidesof the groove back together.

[0018] It is a further object of the present invention to provide adouble angle knife-blade which provides an invisible tear seam byremoving a portion of the skin material at an angle that preventshealing while leaving sufficient material remaining at the base of thegroove or tear seam such that readout on the front side of the skin isprevented.

[0019] It is a further object of the present invention to provide aknife blade design which can be used on both freshly molded as well asaged shells and allow scoring at a reasonably high rate of speed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 is a side view of the preferred ultrasonic knife blade usedin the present invention.

[0021]FIG. 2 is a front view of the knife blade of FIG. 1.

[0022]FIG. 3 is an enlarged view of the knife blade tip of FIGS. 1 and2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023]FIG. 1 illustrates a side view of the preferred ultrasonic bladethat can be used in accordance with the present invention. However, itshould be appreciated that in broad context, any blade that operates toprovide the V-shaped groove described herein is contemplated.

[0024] With attention directed to FIG. 2, as illustrated therein theblade contains a double angle V-shaped configuration. Shown at 10 is thefirst angle cutting surface A which angle is less than the angle ofcutting surface B which is shown generally at 12. In the context of thepresent invention, angle A is preferably between 5-30 degrees and angleB is between 75-150 degrees. In addition it should be understood thatthe present invention contemplates all values therebetween in one (1)degree increments. More preferred ranges therefore include angle A of10-20 degrees and angle B of 90-130 degrees. In a most preferredembodiment, angle A is about 15 degrees and angle B is about 110degrees. Attention is directed to FIG. 3 which illustrates angle A of 15degrees and angle of B of 110 degrees.

[0025] It has been found that the above referenced double angle V-shapeddesign minimizes the weakening line visibility produced therefrom,enhances deployability, while preventing blocking of the skin material.In other words, the skin material is not prone to heal to itself afterthe cutting operation, by virtue of the double angle configuration.

[0026] Preferably, the skin material comprises a thermoplastic polymer,such as poly(vinyl chloride) or polyurethane, thermoplastic elastomers,thermoplastic olefins, and other skin materials utilized for vehicleinteriors. Preferably the blade has a flat front edge (14) as shown inFIG. 1 which also indicates generally the path of knife travel.

[0027] Preferably the groove is 0.045″ wide at the top with 0.020″-0.028″ of material at the bottom thereof.

What is claimed is:
 1. An instrument panel for the interior of a vehiclepassenger compartment equipped with an inflatable airbag device adaptedto be deployed into a passenger space in said passenger compartment,said instrument panel including a covering having an outer surfaceexposed to view and a weakening groove located beneath the outer surfacefor weakening the instrument panel in the form of at least a portion ofan opening at said location of said airbag device, said weakening groovecomprising a V-shaped configuration, wherein said V-shaped configurationcomprises the following general shape:

wherein angle A is less than angle B.
 2. The instrument panel of claim1, wherein angle A is between 5-30 degrees and angle B is between 75-150degrees.
 3. The instrument panel of claim 1 wherein angle A is 10-20degrees and angle B is between 90-130 degrees.
 4. The instrument panelof claim 1 wherein angle A is 15 degrees and angle B is 110 degrees. 5.A method for providing a weakening groove in the underside of a plasticskin to be used as the covering layer for an instrument panel whichoverlies an inflatable air bag device in the interior of a vehicle,comprising the steps of: molding a plastic skin, providing an ultrasonicknife having a double angle blade, contacting the underside of theplastic skin with said double angle knife blade, scoring the undersideof said plastic skin with said knife blade, wherein said double angleblade comprises the following general shape:

wherein angle A is less than angle B.
 6. A cover skin for a component ofthe interior of a vehicle passenger compartment equipped with aninflatable airbag device adapted to be deployed into a passenger spacein said passenger compartment, said cover skin having an outer surfaceexposed to view and a weakening groove located beneath the outer surfacefor weakening the cover skin in the form of at least a portion of anopening at said location of said airbag device, said weakening groovecomprising a V-shaped configuration, wherein said V-shaped configurationcomprises the following general shape:

wherein angle A is less than angle B.